1. Field of the Invention
This invention generally relates to a plasticizer for coating compositions for coating an implantable device such as a drug-delivery stent.
2. Description of the Background
Degradable polymers have found numerous medical applications. One of these applications is to serve as a coating material for stents. However, articles formed of these biodegradable polymers may have undesirable properties, e.g., lack of flexibility, low elongation, too low a drug permeability, or poor processability. One of the commonly used methods to circumvent these shortcomings is to use a plasticizer.
Some most commonly used plasticizers are petrochemicals such as phthalates. Another commonly used plasticizer is epoxided vegetable oil. Some other materials such as small organic molecules, or inorganic materials, such as phosphoric acid can be used as plasticizers. However, many of these plasticizers either lack biocompatibility or have other undesirable properties. For example, petrochemical plasticizers such as phthalates are often toxic chemicals, and epoxided vegetable oil at higher levels may not mix properly into the plastics formulation or may cause plastics formulations to become brittle. Small organic molecules can also be toxic. In addition, they may have high vapor pressures, which may cause them to diffuse out of an article containing such a plasticizer and create shelflife stability issues because the mechanical integrity and the drug release rate, in the case of coating on a drug-delivery stent, will change over time.
Therefore, there is a need for plasticizers for use in coating compositions for coating a medical device such as a drug-delivery stent.
The compositions and the coatings formed thereof disclosed herein address the above described problems and needs.